1. Field of the Disclosure
The present disclosure relates to a light emitting device. More specifically, light modules emitting white light provide light for a liquid crystal display. Additionally, the present disclosure provides a flat light unit for uniformly emitting light by using light modules, and a liquid crystal display device including the light modules.
2. Description of the Related Art
To generate a uniformly progressing light in a plane, a related art flat light unit includes a plurality of cold cathode fluorescent lamps (CCFLs) or a plurality of external electrode fluorescent lamps (EEFLs). The uniformly progressing light may be referred to hereinafter as flat light, which may originate from a flat light unit or backlight unit assembly. The CCFLs and EEFLs are disposed in parallel to generate a flat light having a predetermined area. These CCFLs and EEFLs require relatively large power consumption and may also require a larger or thicker flat light unit to accommodate the size of CCFLs and EEFLs. Additionally, it is difficult to generate a white light by combining a red light, a green light, and a blue light in these CCFLs and EEFLs.
As a result of this disadvantage of the CCFLs and EEFLs, a flat light device may include a light emitting diode (LED). The LEDs may be disposed in a plane. The LED consumes less power and may also be smaller and/or thinner, allowing for an easier change of the size of the flat light unit compared to the CCFLs and EEFLs. Furthermore, a white light may be generated by combining red, green, and blue in the LED. Accordingly, a flat light unit including an LED (hereinafter, a LED-type flat light unit) has become more common.
To generate a white flat light, the LED-type flat light unit includes red, green, and blue LEDs that are arranged alternately in perpendicular and horizontal direction. The red, green, and blue LEDs each include a side emitter lens (not shown). The respective red, green, and blue LEDs arranged in a plane, as illustrated in FIG. 1, emit light in a side direction. In other words, each of the red, green, and blue LEDs emits light that progresses within a predetermined angle range with respect to the plane of the LEDs. In other words, the light emitted from the side of the LEDs includes a range of light rays that pass within a known angular range with respect to the plane.
The red, green, and blue lights emitted within a predetermined angle with respect to the plane are combined to form white light. A diffusion sheet with a high haze and a thick polymethyl metha-acrylate (PMMA) plate are used in the flat light unit to improve the light distribution based on the emission of the light from the sides of the LEDs. The red, green, and blue lights progressing in a diagonal direction change direction into a substantially perpendicular direction by using the diffusion sheet and the PMMA plate. The diagonal direction may include any non-perpendicular direction from an LED. The light is redirected to be more generally perpendicular to the plane. However, a loss of light occurs due to the diffusion sheet. Additionally, the flat light unit may not be slim due to the thickness of the PMMA plate. Furthermore, it may be difficult to maintain a combination balance of the red, green, and blue lights in the white light that is progressing in the generally perpendicular direction from the plane.
These problems may be evident in a liquid crystal display (LCD) device in which the LED-type flat light unit is used as a backlight unit. FIG. 2 is an exploded perspective view of a liquid crystal display device including a related art LED-type back light unit. The liquid crystal display device of FIG. 2 includes a backlight unit 20 disposed below a liquid crystal panel 10. A top case 30 surrounds the edge of the liquid crystal panel 10 and the sides of the back light unit 20.
The backlight unit 20 includes a reflective sheet 24, an optical sheet set 28 and a rectangular main support 26. The reflective sheet 24, optical sheet set 28 and rectangular main support 26 are sequentially stacked on a bottom cover 22. A plurality of LED array substrates 40 are disposed in a common plane on the surface of the bottom cover 22. Each of the LED array substrates 40 includes a plurality of LEDs 42. The LEDs 42 on the LED array substrates 40 are exposed toward the upper surface of the reflective sheet 24 through a corresponding through-hole 24A on the reflective sheet 24. The through-holes 24A may be referred to as holes and are configured to correspond with the LEDs 42.
The plurality of LEDs 42 includes red, green, and blue LEDs. The red, green and blue LEDs each include a side emitter lens (not shown). Each of the red, green, and blue LEDs 42 emits light progressing within a predetermined angle range with respect to a plane parallel to the array substrates 40. The light progresses within a predetermined angle range with respect to the plane so that the red, green, and blue lights from the LEDs 42 is combined to form white light.
The reflective sheet 24 reflects the light that is reflected by the liquid crystal panel 10 back toward the rear of the liquid crystal panel 10 again, thereby improving light usage efficiency. The main support 26 receives and supports the optical sheet set 28 and supports the edge of the liquid crystal panel 10. The optical sheet set 28 causes the white light diagonally (or non-perpendicularly) emitted from the LEDs 42 to progress substantially perpendicular to the plane and towards the rear of the liquid crystal panel 10. To alter the angle of the diagonally emitted light from the LEDs, the optical sheet set 28 includes a PMMA sheet 28A, a diffusion sheet 28B having a high haze, and light concentrating sheets 28C.
The PMMA sheet 28A, as illustrated in FIG. 3, is disposed between the red, green, and blue LEDs 42 and the diffusion sheet 28B. The PMMA sheet 28A changes a progressing direction of red, green, and blue lights that diagonally enter from the red, green, and blue LEDs 42. The diagonal lights are transmitted more toward a perpendicular direction.
The diffusion sheet 28B again changes the direction of the red, green, and blue lights that diagonally entered from the PMMA sheet 28A toward the rear of the liquid crystal panel 10 in a perpendicular direction. The light concentrating sheets 28C causes the red, green, and blue lights from the diffusion sheet 28B to focus on the rear of the liquid crystal panel 10.
Drive integrated circuits (ICs) 12 are installed on or connect to a portion of the edges of the liquid crystal panel 10. The drive ICs 12 drive the liquid crystal panel 10 by a pixel region according to pixel data. The liquid crystal panel 10 transmits a plane white light from the backlight unit 20 (i.e., light concentrating sheets 28C) in an amount corresponding to a gray scale of the pixel data at each pixel region for the display.
Accordingly, a diffusion sheet with a high haze and a thick PMMA plate are used in the flat light unit. The diffusion sheet results in a loss of light such that an image brightness displayed on the liquid crystal panel deteriorates. Furthermore, the loss of a large amount of light unbalances the red, green, and blue lights constituting the white light. This may result in the deterioration of the color clearness of an image displayed on the liquid crystal panel, which reduces image quality. In addition, due to the thickness of the PMMA plate, it may be difficult to reduce the thickness of the liquid crystal display device.